xe2x80x9cA portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.xe2x80x9d
The quest for a xe2x80x9csolidification timexe2x80x9d began in the early 1950""s when Doehler-Jarvis Corporation constructed a 2000-ton machine demonstrating the capability to produce castings weighing more than 70 pounds. Previous die casting machines were limited to 800 tons of locking force, maximum and could only produce castings weighing up to approximately 2 pounds. The xe2x80x9csolidification timexe2x80x9d it was believed would indicate on the basis of the wall thickness, the alloy temperature and the die temperature time, the maximum time allowable to fill a casting of given weight (volume). The hypothesis was that the temperature of the solidifying metal in the thinnest wall of the casting could not fall below the solidus point of the alloy before the cavity was filled and a high static pressure applied to the molten metal.
Perhaps the first reference to the concept of xe2x80x9csolidification timexe2x80x9d in relation to xe2x80x9cfill timexe2x80x9d can be found in H. H. Doehler""s 1951 book, xe2x80x9cDie Castingxe2x80x9d, McGraw-Hill Book Company, in two statements. xe2x80x9cIn the final analysis, the last portion of metal necessary to complete a casting must enter before the portion that entered first has solidified. It therefore follows that injection speed is one of the most important variables in die casting.xe2x80x9d Doehler determined a relative injection speed for a number of zinc and aluminum alloys, stating which alloy should be injected faster than another does but gave no absolute values.
Subsequent researchers produced solidification times either based on empiricism or formulated equations based upon a rationale of classical metallurgy. In 1957 J. Lapin formulated a table for the xe2x80x9csolidification timesxe2x80x9d of various wall thickness and metals in his xe2x80x9cAnalytical Approach to Gate Designxe2x80x9d, This empiricism was one of the earliest attempts to quantify a number for the time in which a die cavity had to be filled. Following the postulate that to produce a high quality die casting the die caster should fill the die cavity before the alloy reaches the solidus or final freezing temperature, F. C Bennett, Dow Chemical Company, in xe2x80x9cDesigning Die Casting Dies to Work on Early Shotsxe2x80x9d presented an equation in November 1966 for the filling time. Bennett""s equation assumed half of the thermal energy above the solidus was concentrated at the mid-plane of a given wall and calculated the time for this energy to drop through a gradient determined by the molten alloy-die surface temperature difference.
Bennett""s equation is: xcex8=q*x/(k*S(tmxe2x88x92td))
where: xcex8=the maximum fill time in seconds, S=surface area (square inches),
tm=mid plane alloy temperature (xc2x0F.), td=die surface temperature (xc2x0F.)
x=midplane-to-die distance (inches), q=the heat flow during fill time xcex8, (Btu)
In 1965, culminating three years of research sponsored by the American Foundrymen""s Society, the American Die Cast Institute, and the International Lead, Zinc Research Organization, Wallace, J. F. and Stuhrke W. F., Case Institute of Technology xe2x80x9cGating of Die Castingsxe2x80x9d, developed the constant flux model for heat flow in a die casting die. A series of equations were formulated which permitted the prediction of temperature-time curves for the steel die surface to which the heat from the molten alloy was being transferred. The equations of the researchers were erroneously based on the linear flux model of Franz Neumann, xe2x80x9cDie partiellen Differentialgleichungen der mathematischen Physic, Wallace, and Stuhrke placed a thermocouple in the surface of a die casting die which cast alternatively xe2x85x9 inch or xc2xc inch plates of zinc alloy, Zamak 3 or aluminum alloy 380. Relying on classical metallurgy, i.e. 1) that the superheat (heat above the liquidus) flowed out of alloys before the heat of solidification and 2) the alloys must fill the cavities while their temperature is above the classical solidus the Case researchers searched for an impediment to the heat transfer from alloy to die. This study produced considerable quantitative and supportive data, which has aided the die cast industry even to the present date but did not result in a scientific basis for the solidification of metals in a die casting die.
Also accepting the classical metallurgy hypothesis, which necessitated a xe2x80x9cfilm coefficientxe2x80x9d. was C. W. Nelson, Dow Chemical Company, xe2x80x9cNature of Heat Transfer at the Die Facexe2x80x9d. To conduct his study with the goal of finding a xe2x80x9csolidification timexe2x80x9d Nelson mounted five thermocouples in a die casting die which produced a 3xe2x80x3xc3x978xe2x80x3xc2xcxe2x80x3 thick magnesium AZ91 alloy plate similar to the Wallace work and produced die temperature recordings. One of the thermocouples was exposed at the surface and measured the AZ91 boundary temperature as the casting die would sense it. Based on the die surface temperature recordings Nelson drew a magnesium boundary surface profile above the thermocouple die temperature curve for the time frame that he perceived. The assumption was made the magnesium curve commenced at the liquidus line and decayed from this point. Nelson then proceeded to calculate the xe2x80x9cfilm coefficientxe2x80x9d factor xe2x80x9chxe2x80x9d for the superheat, the matrix, and finally the solidified cooling magnesium.
In spite of the inability to demonstrate a sound technical xe2x80x9csolidification timexe2x80x9d devices had been produced which could measure the hydraulic pressure in the cylinder used to inject the metal into the die. The generic name for such a device is hydrauliscope and in its simplest versions consists of a pressure transducer located in the inlet of the injection cylinder with the analog output of the transducer converted to digital then being fed to a computer. The computer display of the transducer output will have the pressure variable plotted on the vertical axis and time on the horizontal. Significant events in the injection cylinder displacement of molten alloy correlate with pressure changes. A pressure rise occurs when the injection cylinder and piston have traveled such that molten metal now must be displaced through the ingate orifice to the casting and the resistance to the cylinders movement increases. When the cavity has filled and further displacement of metal is not possible the kinetic energy of the moving injection mechanism and fluid in the cylinder is dissipated and its dissipation is revealed by a sharp rise in the pressure followed by a damped oscillation of the pressure. The xe2x80x9cfill timexe2x80x9d is therefore the difference between the readily detectable sharp rise signaling the die cavity is full and the earlier pressure rise, well recognized as the time when metal commences to flow into the cavity.
Without considerable precision in the determination of the xe2x80x9csolidification timexe2x80x9d the xe2x80x9cfill timexe2x80x9d must depend on the experience of the user. Following the Nelson work in 1970 the quest for the xe2x80x9csolidification timexe2x80x9d was largely abandoned until the inventor decided to readdress the problem. In 1961 the inventor attempted to solve the problem on the basis of the concept of a temperature gradient between the center of an alloy wall and the die surface but found due to the unavailability of elevated temperature properties for the die cast alloys and restricted computer capability it could at best be a crude approximation. By 1996, computers with state of the art hardware and software were available at the retail level for several thousand dollars, which were more powerful than those costing several millions in 1961.
Essential to the advancement of a science in the transient supercooling and solidification of metal in a die casting die was the formulation of a mathematical analysis that was not an empiricism and had its roots in traditional mathematical approaches to heat flow problems. In late 1996 the mathematical approach to a solution to the solidification of metals in a die casting die through a unique dual Fourier series analysis had been demonstrated to be feasible, and by the first quarter of 1998 a software program had been copyrighted. One of the Fourier series analyses gives the temperature for the alloy as a function of time and depth, a second yields time vs. depth and temperature in the die material, a third equation calculates the boundary surface between the die and the solidifying alloy and a fourth calculates the heat remaining in the alloy wall above the xe2x80x9cdynamic solidusxe2x80x9d defined below.
Unfortunately, the initial mathematics used classical metallurgy and a film coefficient due to the convincing work of the researchers of the late 1960""s. This software gave excellent results in duplicating the die surface temperatures recorded by Nelson in his work with magnesium alloy AZ91B and Wallace and Stuhrke""s thermocouple work with aluminum alloy SC84. Both of these alloys have relatively broad temperature differences ( greater than 100xc2x0 F.) between their liquidus and solidus temperatures. The classical metallurgy thesis and the xe2x80x9cfilm coefficientxe2x80x9d theory failed, however, when alloys with narrow differences (15xc2x0 F.) between the liquidus and solidus existed such as aluminum 13 alloy and zinc alloy AG40A. The mathematics showed these highly castable alloys had to be fluid while the boundary temperature between the alloy and the die, during the entire xe2x80x9cfillingxe2x80x9d time were below the classically defined solidus. This work resulted in the proof that molten metals injected into a die casting die are supercooled i.e. they possess the properties of a liquid even though the metal""s temperature is below the classical metallurgical solidus. All of the phenomena, which caused previous researchers to hypothecate a film coefficient, could be explained on the basis of supercooling and this became one of the physics postulates of the inventor.
Thus the hypothesis that the temperature of the solidifying metal could not fall below the solidus point of the alloy before the cavity was filled was demonstrated to be incorrect.
Further, the inventor""s science and software program showed the process by which alloy walls temperatures reach a value at which liquid metal can not exist.
With the xe2x80x9cfilm coefficientxe2x80x9d hypothesis shown to be invalid, based on the inventor""s mathematics the inventor then formulated the remaining physics postulates for the solidification of metals in a die casting die. These are set out in eleven physics postulates, and are included with the mathematics and a syntagma in a literary copyrighted work entitled xe2x80x9cIsoclinesxe2x80x94A Treatise on the Solidification of Metals in a Die Casting Die(copyright) 2000xe2x80x9d with that copyrighted work in its entirety available for downloading from the inventor and author""s WebSite. The most important facet of the treatise to this invention is the inventor""s development of the uniqueness of the boundary surface temperature between the solidifying alloy and the die and the laws governing it as expressed in the mathematical equation for the boundary temperature.
It is not uncommon in the die casting process to use a hydrauliscope to produce a pressure versus time graph of the injection cylinder hydraulic pressure. Prior to formulation of the inventors mathematics and physics and this invention, there was not a scientifically based solidification thesis on which to base the speed of injection of alloys in pressure die casting. The use of hydrauliscope recordings was an empirical one. When acceptable castings were obtained the hydrauliscope recording of the pressure-time relationship used to produce that casting was preserved and set as an empirical standard. Hydrauliscopes are also used for detecting cylinder piston leaks and inadequate pressure. The establishment of a xe2x80x9cfilling timexe2x80x9d was entirely based on the die casters experience with a tendency to believe faster was better since a scientific determination of the solidification in a die casting die did not exist. The tendency for faster injection, however, does have a penalty associated with it, for if the injection is too fast and without some losses of heat the extremely fluid molten metal cannot be contained in the die. There are no hydraulic seals in a die casting die for shutting off the escape of liquid metal under high pressure, and the prevention of the leakage of liquid metal relies upon the solidification of microflash along all parting lines for forming a type of gasket. If the metal is injected faster than this microseal of flash can develop, the hydraulic cylinder will xe2x80x9cbottomxe2x80x9d against the ejector die after forcing liquid metal beyond the confines of the die.
The fallacy of xe2x80x9cfaster shots are betterxe2x80x9d is compounded when it extends itself to believing that larger machines with greater locking force will somehow overcome the fact of the non-existence of hydraulic seals in a casting die. The lack of an explanation for the metal solidification phenomena in a die casting die has resulted in large aluminum castings being produced in many instances on 3500 ton die casting machines which can readily be produced at higher production rates and in better quality from 1750-2000 ton die casting machines. The higher temperatures of dies producing castings in the faster cycling smaller machines will result in better quality at lower cost. Further the faster cycling smaller machines possible with a scientific use of this invention obviates the need to heat oil based substances and circulate them through the die to raise its temperature to an acceptable temperature range.
At the other end of the spectrum an excessively long duration for the injection of molten metal into the casting die will result in the metal being so viscous, due to its partial solidification, as to dissipate the injection pressure without filling the cavity.
In the next two paragraphs are definitions of terms that will be used throughout.
By definition, Isoclines, referenced herein are cooling lines of constant depth in a casting wall of metal solidifying in a die casting die with the temperature of these lines being calculated and plotted as a function of time. Referenced herein is the inventor""s copyrighted software program, xe2x80x9c(copyright)1998 Isoclinesxe2x80x9d, for calculating Isoclines through the mathematics and the physics of the inventor which has the ability to alternately receive the transient boundary temperature signal from a die surface-mounted thermocouple or calculating the boundary with one of the equations of Isoclines. The computer software program, xe2x80x9c(copyright)1998 Isoclinesxe2x80x9d, uses Microsoft Excel spreadsheets for calculations, data storage, drawings, and plotting and employs Microsoft Visual Basic as the programming language to order the calculation of Isoclines equations. xe2x80x9c(copyright)1998 Isoclinesxe2x80x9d software will be defined herein as simply xe2x80x9cIsoclines(copyright)xe2x80x9d. The development of programmable software languages and techniques has kept pace with the rapid development of computers and there are numerous xe2x80x9ccannedxe2x80x9d software programs, which can perform the calculation of the inventor""s equations. The use of any of the commercially available computers containing a software and program language which will perform the calculations of the inventor""s equations will be said to be a xe2x80x9cpreferred computer software programxe2x80x9d or simply a xe2x80x9cpreferred software programxe2x80x9d. Stored in the preferred computer software program are the thermal properties of the alloy being cast as well as the thermal properties of the die material. The pouring temperature, the initial die surface temperature, and the wall thickness of the casting are also stored in the software program. The die thickness is taken as thick enough that in time interval for injection, the heat flowing into the die is insufficient to affect the temperature at that depth. This has been shown to be less than 10 times the casting wall thickness, reasonably attained in any practical die casting die.
The xe2x80x9cfill timexe2x80x9d is defined earlier as the difference between the point of the characteristic rise in the hydrauliscope pressure plot associated with the cessation of the metal flow into the cavity minus the earlier pressure rise associated with the increased resistance encountered when molten metal begins to flow through the ingate to the cavity. The dynamic liquidus is defined as the temperature at which solid first forms in the transient solidification of metal in a die casting die and is a function of the flux rate across the boundary. Lastly, the dynamic solidus is defined as the temperature at which the last of any liquid metal has become solid in the transient solidification of metal in a die casting die and is a function of the flux rate. The xe2x80x9cdynamic solidusxe2x80x9d may be distinguished by a plateau but may also need to be determined by the degree of convergence of the Isoclines.
To obtain the graph of the boundary temperature of Isoclines from the mathematics of the inventor the thermal conductivity of the alloy must be known or developed as well as the xe2x80x9cdynamic liquidusxe2x80x9d. The high temperature thermal properties of the die material must also be known but in general for the commonly used die material H-13, these are readily available. From a single charted thermocouple recording of the boundary interface between the die and the alloy the alloy conductivity as a function of temperature can be determined and Isoclines can then be calculated for other wall thickness, initial die temperatures and alloy pouring temperatures.
Isoclines now permits the judgment for a xe2x80x9cfill timexe2x80x9d to be made on a scientific basis such that the filling of the cavity is optimally achieved between the dynamic liquidus and dynamic solidus and further aiding the judgment of when to start the intensification cycle and how long to maintain this higher pressure. Injection pressure intensifiers are hydraulic pressure multiplier devices and their use is typical rather than novel.
The definition of xe2x80x9cartxe2x80x9d is (a) A non-scientific branch of learning, (b) A skill that is attained by study, practice, or observation. The field of die casting is replete with examples of the art of using thermocouples to achieve an improvement of sorts in the process. There are, however, no precedents in the die casting field for the application of a thermocouple based on a science for determining the solidification process of injected metals to control the process as McDonald""s process improvement discloses herein. In fact the solidification xe2x80x9ctimexe2x80x9d itself was the subject of speculation until the publication of the inventor""s treatise. With the physics postulated in February and March of 2000 a science in the solidification of metals in a die casting die was born.
Prior xe2x80x9cartxe2x80x9d, however, does exist for the use of thermocouples to xe2x80x9ctriggerxe2x80x9d a process control in various casting operations such as turn on or off a water line. As far back as the 1950""s some practitioners of die casting have even used computers to affect process control, however, they all were artful uses.
Dow Chemical Co. in 1971 received U.S. Pat. No. 3,583,467 that had two thermocouples embedded in the die to control water-cooling to maintain the die temperature in a specific range. While the goal of the use by Dow of thermocouples was to balance the heat in the die never the less the temperatures to which Dow was attempting to control that balance were experienced based. The data from the thermocouples were not subjected to analysis for improved control and the thermocouples were used only as limiting devices.
A similar use is shown in U.S. Pat. No. 5,363,899 of Takagi et al. Takagi states column 5 line 64 xe2x80x9cThe thermocouple 2 is held by a spring to ensure close contact of the tip of thermocouple 2 with the die at the measuring point.xe2x80x9d In column 2, line 8, Takagi et al notes that the thermocouple xe2x80x9cmeasures a die temperaturexe2x80x9d and at line 13 states that this temperature xe2x80x9ccompares with a reference value.xe2x80x9d It is clear Takagi""s method involves empiricism""s and xe2x80x9cartxe2x80x9d and a computer is used only for comparative purposes and elimination of human error. While it can control human error Takagi""s empiricisms are subject to error and do not have the capability of science. It is clear McDonald""s method represents a useful improvement over Takagi""s method of comparing current data from thermocouples with reference values. No attempt is made in Takagi""s method for the use of a computer to do analysis on the thermocouple data for improved performance and it serves only as a limiting device.
McDonald""s method can determine the necessary alloy solidification pattern from use of thermocouple contact with the casting at the die surface of from an initial die surface temperature just prior to the die closing. The preferred method is to determine the transient boundary temperature from a die-surface mounted thermocouple providing data throughout the solidification temperature range of the alloy. To calculate the boundary temperature for the solidification range of the alloy, there are alternatives to a die surface thermocouple for determining the initial die temperature. These are contact with a surface pyrometer at the desired location or directing an optical pyrometer at the chosen location the instant before the machine closes. Flexibility in selecting the location is the greatest advantage of a pyrometer method. Preferred, however, is the transient temperature data for the casting surface from a die surface embedded thermocouple i.e. essentially the interface temperature between the die and the molten alloy. This data subjected to analysis by a computer with the mathematics and physics of McDonald in a computer plots the solidification process, Isoclines, as a function of time and depth in the wall of the casting at the point where the thermocouple is located. This permits the setting either manually or automatic of the injection time and intensification time of a subsequent casting on the basis of science, an improvement over the art and empiricism of Takagi.
Booth in patent U.S. Pat. No. 3,842,893, teaches a control on the injection parameters of liquid metal in the low pressure permanent mold process which due to the refractory coating on the mold has a solidification time greater by 100 fold than the solidification time in pressure die casting. Booth""s patent is in the permanent mold process category and not die casting as referenced in the United States. Booth does not claim to reference a data set of temperatures. Specifically Booth teaches verbatim column 1 line 52: xe2x80x9cThus . . . sensing when the casting material has reached a desired temperature, e.g., when it has solidified, this will be called the datum point, and thereby generating a signal and using this signal to terminate the application of gaseous pressure preferably automatically and preferably also to initiate the die opening sequence either immediately or after a set delay period.xe2x80x9d Booth uses a thermocouple to sense when the metal in the die has solidified while McDonald""s method analyzes thermocouple data before the metal has solidified and with his mathematics and physics determines how the metal is solidifying so that the metal can be properly injected in a subsequent cycle. Booth uses a thermocouple solidus temperature detection to initiate an action where McDonald""s invention is no longer interested in the thermocouple data after a solidus would be reached. With consistency and repeatability key elements in the production of high quality die castings the next casting produced by this invention benefits materially from control of the injection based on the Isoclines from the previous cycle.
McDonald""s method is basically superior in consistency to that of Booth by virtue of the science applied to the use of a thermocouple when calculations are made using the mathematics and physics of the Isoclines Treatise to determine the split second solidification processes development.
In U.S. Pat. No. 4,493,362, Moore et al., teaches process control and injection control through the use of numerous thermocouples. Moore, however, goes further than Takagi and presents a formula at column 7 line 57 for the cavity fill time not the solidification of the alloy using a measured data point temperature for the metal in the gate runner in his formula. Moore makes no claims that his formula relates to the progress of solidification in the die cavity. It is presumed this is an empirical formula for nowhere does he indicate the origination of the formula. This empirical formula can be found to be lacking for it does not contain a basis for assuring that the injection will occur prior to the passing of the dynamic solidusxe2x80x9d time, or for that matter any solidus. Moore""s formula uses a liquidus temperature for the alloy. Additionally, the formula fails to incorporate the traditional thermal properties of specific heat, density, thermal conductivity and diffusivity of the alloy and the die material essential to determine the solidification taking place in the die cavity. Moore has several thermocouples, 112, 114, column 5 line 33, embedded deeply in the die casting die essentially serving the same purpose as Takagi et al. registering data points within the die and not at the surface of the casting. Moore also has a thermocouple 96 at column 5 line 8 whose function is to control the quantity of metal transferred from the furnace to the cold chamber. Finally, Moore has a thermocouple 80 column 4 line 65 located at the impact bushing that functions to sense the temperature of metal (a data point) flowing from the cold chamber to the die cavity. Nowhere does Moore teach the utilization of a thermocouple in contact with the molten casting wall at a boundary surface with the die. Therefore, Moore cannot determine the transient temperature rise and fall which are indicative of the xe2x80x9cdynamic liquidus and solidusxe2x80x9d of the scientific method of McDonald. Even if Moore did detect the transient boundary, he nowhere indicates in describing his process improvement, that his method has a mathematical equation to analyze such a boundary and produce a solidification pattern.
None of the cited prior art patents uses a thermocouple method, which is truly scientific, nor do the inventors claim the use of a science in the solidification process of the metals cast in applying their art. Each relies on empiricisms, prior experience parameters, and xe2x80x9cartxe2x80x9d. None applies a science-based mathematics and physics to the use of a thermocouple.
It should finally be pointed out that Moore and Tajagi use a thermocouple to record a die temperature and they never suggest they desired or intended to use a thermocouple to detect a casting temperature while it is explicit in McDonald""s invention that a casting surface temperature is desired from a thermocouple imbedded in the surface of the die.
During the last fifty years there have been a number of massive usage changes between the commonly die cast alloys of zinc, magnesium and aluminum driven by price or scarcity or both. To convert the production of, for example, an automotive transmission case from aluminum to magnesium would require a considerable learning curve for those producers using empiricism or reference values before their process could have affective controls. McDonald""s method relies on science and would optimize injection performance almost immediately and that optimized level based on science in every instance would be superior to empirically optimized performance and the invention disclosed herein is a useful process improvement.
The following presents a method of improving the production of die castings which utilizes the mathematics derived and the physics discovered in the inventors copyrighted work entitled xe2x80x9cIsoclinesxe2x80x94A Treatise on the Solidification of Metals in a Die Casting Die(copyright)xe2x80x9d 2000.
The broad object of this invention resulting from the mathematics and physics of the solidification of metals in a die casting die, developed by the inventor and embodied in Isoclines(copyright) is to replace guesswork and empiricism with a science for establishing and controlling the fill time i.e. the injection speed and intensification of molten metal into a die casting die, providing a method for more consistent die casting quality as largely typified by improved soundness. However, the method disclosed provides many other advantages as well, not the least of which is a safer process.
A specific objective of this invention is to assert control of the injection process through Isoclines determined from a calculated alloy-die interface boundary temperature whereby the essential input of the initial die surface temperature into the inventor""s equation for determining the transient boundary temperature, is determined by a die surface thermocouple, a surface contact pyrometer or an optical pyrometer. For this objective and all objectives the alloy pouring temperature, the alloy thermal properties, the die material thermal properties, and the casting wall thickness must all be stored in the preferred computer software program.
A specific and preferred object of this invention is to utilize the uniqueness of the alloy-die interface temperature boundary, i.e. the casting surface temperature, discovered by the inventor, by feeding a die surface mounted thermocouple output into the preferred computer software program to replace a calculated less accurate alloy-die temperature boundary for establishing control of the injection speed and intensification of molten metal. The process controlled in this manner as opposed to a calculated boundary, will reduce error in the transient temperature emanating from alloy and die material thermal properties. An objective of this invention is to use the digital input to the preferred software program from the alloy-die temperature boundary thermocouple to obtain more accurate calculations of Isoclines than is arrived at using published and derived thermal properties of the metal alloy and the die material for a calculated boundary temperature.
A more specific objective of this invention is to control the duration of time for the injection of metal into a die casting die i.e. the fill time, through a comparison of this fill time as traditionally displayed by a hydrauliscope with the convergence of calculated Isoclines or the dynamic solidus plateau for the cooling alloy. Pragmatically, the convergence of Isoclines or the dynamic solidus signals the end of solidification and the comparison recognizes the low probability of injecting metal into the die if all that remains is solid metal flowing in the cavity. The cavity should be filled in a time less than it takes for the solidifying metal to cool to the dynamic solidus.
It is an objective of this invention to use the preferred computer software program to calculate the heat flow out of the alloy as a function of time, or alternatively the heat remaining in the molten alloy above the dynamic solidus at any given time to aid in determining and setting the xe2x80x9cfill timexe2x80x9d.
Similarly, the accuracy of the calculated quantity of heat diffused to the die, as a function of time by the preferred software program will be improved by using the digital input from the alloy-die temperature boundary thermocouple to the preferred computer software program to make this calculation for controlling the fill time.
A further object of this invention is the extension of the range of parts that can be produced by the die casting process through the improved soundness possible in an embodiment of this invention.
Another objective of this invention also is to provide improved safety by assuring the cavity is never filled so fast as to have been completed in the interval of the dynamic liquidus plateau since the fluidity is extremely high at this time and would permit hot liquid metal to be forced out through the parting plane of the die i.e. the action known as xe2x80x9cspittingxe2x80x9d.
The injection speed is a function of the injection cylinder pressure. An object of this invention is to avoid undue pressure i.e. excessive injection speeds through a more scientific determination of the required fill time and can result in smaller faster die casting machines being used for a given casting and thereby greater productivity and reduced scrap.
It is an object of this invention that a pressure transducer in the injection cylinder be fed to the preferred software program so that it can be plotted to validate the fill time through a comparison with the convergence of the Isoclines, the dynamic solidus, or the calculated heat remaining in the alloy above the dynamic solidus.
This invention is for controlling the duration of time for the injection and intensification of metal into a die casting die through the inventors mathematics and physics thereby improving the die casting process. The controls possible with the inventors equations permits a more scientific determination of the machine size for a given casting, improved quality, improved safety, greater productivity, and reduced scrap.
It is an object of this invention to use the alloy-die temperature boundary data input along with the given conditions, certain thermal properties of the alloy and the thermal properties of the die material stored in the computer software to determine the thermal conductivity of the molten alloy above the dynamic solidus. The inventors equation for the boundary temperature below show that the conductivity of the alloy above the solidus can be obtained by fitting a calculated boundary plot to the plot of the die surface-mounted boundary thermocouple output for the same initial conditions and therefore has value as a scientific tool. The thermal properties of the die material must be known as a function of temperature for this objective. Producers of die materials which are in the main steel companies and technical societies for materials research have published such thermal properties. The mathematics and physics of the author-inventor and the copyrighted software, applied to the die casting process in this invention, are key elements in a hitherto non-existent science on the solidification of metal in a die casting die.
Other objects and advantages will be obvious from the following Detailed Description of the Invention.